# CVE-2026-115506: libexpat through 2.9.0 Denial of Service via Billion Laughs Detection Delay


- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 22 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** AZL-110546, AZL-111014, DEBIAN-CVE-2026-115506, ECHO-77e5-0c9b-7930, GHSA-j83x-34mv-v962, ROOT-OS-DEBIAN-13-CVE-2026-115506, UBUNTU-CVE-2026-115506

## What is CVE-2026-115506?

CVE-2026-115506 is a high-severity vulnerability in libexpat, published on 22 Oct 2026. 

### Official description

libexpat through 2.9.0 contains a denial of service vulnerability because billion laughs protection in accountingDiffTolerated() in xmlparse.c detects entity amplification too late. Attackers can supply a moderately sized XML document with a large DTD and nested entity expansions to consume tens of seconds of CPU per parse.

Weakness: CWE-776 (Improper Restriction of Recursive Entity References in DTDs)

## Which versions are affected by CVE-2026-115506?


## How do I fix CVE-2026-115506?

Upgrade to a fixed version.

## Is CVE-2026-115506 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-115506 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-115506 and fix it if it is affected.

What it is: CVE-2026-115506 is a high-severity vulnerability in libexpat, published on 22 Oct 2026. 
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-115506 exists.

Affected product: libexpat. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-115506/ (Markdown: https://insights.sbomify.com/CVE-2026-115506/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-115506
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-115506
- OSV: https://osv.dev/vulnerability/CVE-2026-115506

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-115506/
Summaries are generated and may contain mistakes; the official description above is the record.